Aminobutyraldehyde dimethyl acetal (ABAA) is an amine which can be incorporated into polymers to provide crosslinkable functionality useful in coatings formulations. The advantage of coatings technology based on ABAA and other aminoalkylaldehyde alkyl acetals is that it can avoid the use of formaldehyde-based crosslinkers. Legislation requiring reduction of such formaldehyde emissions has become increasingly stringent and coatings formulators and resin manufacturers have become receptive to alternative, more environmentally benign technologies.
ABAA, and other aminopropionaldehyde acetals are typically produced by hydrogenation of the corresponding nitrile, a material in turn produced by catalytic hydroformylation of acrylonitrile in an alcohol solvent. The initially-formed cyanopropionaldehyde is converted under the reaction conditions to the cyanopropionaldehyde acetal by reaction with an alcohol. The reaction product is distilled to remove impurities and then hydrogenated.
The following patents are relevant to the hydrogenation of nitriles:
U.S. Pat. No. 2,449,036 discloses the manufacture of primary amines by the catalytic liquid phase hydrogenation of the corresponding nitrites. In an effort to avoid the formation of secondary and tertiary amines, hydrogenation of nitrites has been carried out in the presence of ammonia or in the presence of substances capable of liberating ammonia. One of the problems was that the addition of ammonia decreased the partial pressure of hydrogen in the reactor which lead to lower rates of reaction than in hydrogenation reactions performed in the absence of ammonia. Cobalt catalysts in combination with an alkali metal hydroxide, e.g., sodium, potassium or lithium hydroxide, or quaternary ammonium bases were found to result in high yields of a primary amine without the concomitant problems associated with the use of ammonia.
U.S. Pat. No. 3,427,356 discloses the preparation of 1,3-propylenediamines by hydrogenating .beta.-aminopropionitriles in the presence of ammonia at temperatures below 200.degree. C., the catalyst for such hydrogenation being cobalt or nickel. The patentees point out that a small amount of a manganese compound dissolved in the hydrogenation mixture enhances the activity of the catalyst with little decomposition of the catalyst or deposition of the polymers thereon.
U.S. Pat. No. 3,896,173 discloses a two stage catalytic hydrogenation of unsaturated dinitriles using ruthenium or nickel as the catalyst. In the process, ammonia is used in the first stage catalytic hydrogenation wherein the nitrile is reduced to the amine. This hydrogenation is followed by a second stage hydrogenation where the ethylenic unsaturation is hydrogenated. Conventional hydrogenation catalysts are deemed suitable for the two stage hydrogenation and these include ruthenium, Raney nickel, and the like.
U.S. Pat. No. 4,375,003 discloses an improved process for preparing primary amines from an aliphatic nitrile and hydrogen. Raney cobalt is used as the catalyst. To avoid the use of ammonia and other bases in an effort to produce primary amines in high yield, a small amount of alkali metal hydroxide is added. The catalyst employed is a Raney cobalt catalyst incorporating from 2-35 weight percent aluminum with a cobalt aluminum alloy being contacted with an aqueous medium containing dissolved alkali metal hydroxide.
European 0 316 761 discloses a process for producing N,N-dimethyldiamino-propane by the catalytic hydrogenation of N,N-dimethylaminopropionitrile in the presence of ammonia and one or more alkaline earth oxides. Raney cobalt is the preferred catalyst.